1. Field of Invention
The invention relates to an automatic transmission with a hydraulic control apparatus.
2. Description of Related Art
Conventionally, an automatic transmission used in a vehicle such as an automobile and the like has a variable speed gear provided with a planetary gear unit and the like. The variable speed gear is provided with a plurality of frictional engagement elements such as a clutch, a brake and the like. The variable speed gear is structured so as to selectively output a rotation from gear elements such as a sun gear, a ring gear, a carrier and the like in the planetary gear unit so as to achieve a plurality of shift ranges by engaging and disengaging each of the frictional engagement elements in accordance with a predetermined combination.
The frictional engagement elements are engaged and disengaged by operating a hydraulic servo in a hydraulic circuit. Further, the hydraulic servo has a hydraulic servo drum having an outer peripheral wall and an inner peripheral wall, an annular piston slidably fitted within the hydraulic servo drum and the like. The hydraulic servo is structured so as to move the annular piston by supplying oil to and discharging oil from an apply oil chamber formed between the hydraulic servo drum and the annular piston, thereby engaging and disengaging the frictional engagement elements arranged in opposition to the annular piston.
Further, various kinds of solenoid valves, switch valves and the like are arranged in the hydraulic circuit. A predetermined switch valve is switched by turning on or off a solenoid of a predetermined solenoid valve, and a hydraulic pressure is supplied to the hydraulic servo connected to the switch valve. For that purpose, respective solenoids are mounted on valve bodies constituting the hydraulic circuit, and the respective solenoids and the control apparatus of the automatic transmission are connected by a wire connector unit.
However, in the related art, when an external force and the like are applied to the wire connector unit, there is a case that the wire connector unit comes off from the control apparatus and the like. However, in this case, the structure is made such that a failsafe operation is executed so as to drive the vehicle in a predetermined shift range, for example, a third speed.
However, in the conventional automatic transmission mentioned above, when the failsafe operation is executed and the speed is fixed in a third speed while the vehicle is running in a shift range in a high speed side such as a fourth speed, fifth speed and the like, a braking force of an engine brake becomes large, and a shift shock applied to a driver is increased.
Also, for example, in the case of driving the vehicle on a climbing road with a large inclination while the speed is fixed in the third speed, a load applied to the variable speed gear of the automatic transmission is increased, and a temperature of an oil, that is, an oil temperature becomes, for example, suddenly high.
The invention thus provides an automatic transmission according to an exemplary aspect of the invention with a plurality of hydraulic servos which respectively engage and disengage a plurality of frictional engagement elements, a first solenoid valve for gear shifting which is used for generating a hydraulic pressure supplied to a predetermined hydraulic servo, a second solenoid valve for lock-up which is used for generating a hydraulic pressure supplied to a fluid transmission apparatus for executing a lock-up, a hydraulic control apparatus, a first connector which connects the first solenoid valve and the hydraulic control apparatus, a second connector which connects the second solenoid valve and the hydraulic control apparatus, a failsafe mechanism which achieves a predetermined shift range in a high-speed-side when the first connector is disconnected and a gear shift processing mechanism which achieves a predetermined shift range among a plurality of shift ranges when the second connector is disconnected.
The automatic transmission according to a preferred form of the exemplary aspect of the invention is further provided with a shift range changing mechanism for achieving, after the predetermined shift range in high-speed-side is achieved when the first connector is disconnected, a predetermined shift range in a lower-speed-side than the predetermined shift range in the high-speed-side.
An automatic transmission according to another preferred form of the exemplary aspect of the invention is provided with a lock-up processing unit which executes a lock-up of the fluid transmission apparatus when the first connector is disconnected.